Conventional power supplies mounted on high-frequency heating apparatus were heavy and large. It has been therefore demanded to make the power supplies smaller in size and lighter in weight. To this end, in various kinds of present fields, switching has been aggressively applied to power supplies to thereby make the power supplies smaller in size, lighter in weight and lower in price. In high-frequency heating apparatus for cooking foodstuffs by microwaves generated by magnetrons, there was a request to make power supplies for driving the magnetrons smaller in size and lighter in weight. The request was realized by switching in inverter circuits.
Of the inverter circuits, a high-frequency inverter circuit aimed at by the present invention is based on a resonance type circuit system using switching devices, in which an arm of a bridge is formed by two transistors (for example, see Patent Document 1).